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This converts to using the skia::mojom::Bitmap serialize functions to
turn an SkBitmap into a string and back for putting into a base::Value
and sending over IPC.

TBR=senorblanco

Bug: 1144462
Change-Id: I10f28bff10aed703e59c500e7f4668f557b51785
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521203
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825007}